1. Field of the Invention
The invention relates to a three-dimensional shape data creating method for creating three-dimensional shape data of a three-dimensional object created by a designer, or the like, from a sketch of the three-dimensional object, and also relates to an apparatus for creating three-dimensional shape data and a computer-readable storage medium.
2. Description of Related Art
Various methods for creating three-dimensional shape data of a three-dimensional object created by a designer, or the like, from a sketch of the three-dimensional object, have been proposed, as disclosed in Japanese Patent Application Publication No. 6-149943 (JP-A-6-149943), Japanese Patent Application Publication No. 2004-206262 (JP-A-2004-206262), Japanese Patent Application Publication No. 6-301751 (JP-A-6-301751), and Japanese Patent Application Publication No. 10-269380 (JP-A-10-269380). For example, JP-A-6-149943 discloses a method of creating three-dimensional shape data of a three-dimensional object, using a perspective view (sketch) of the three-dimensional object in which a cross-section line(s) that appears when the object is cut in a given plane is/are depicted, wherein the three-dimensional shape data is created by obtaining a plane equation representing the plane in a three-dimensional space of an orthogonal coordinate system, from a disappearance point corresponding to the above plane relative to the perspective view, and projecting the cross-section line(s) onto the plane represented by the plane equation.
Also, a method of creating three-dimensional data by reading perspective views in the form of two or more hand-written sketches, and processing data obtained from the sketches, is disclosed in, for example, JP-A-2004-206262.
In the related art as described above, even though the sketch drawn by a designer, or the like, is a mathematically inaccurate perspective drawing, three disappearance points are obtained and the viewpoint position and three-dimensional space are defined on the assumption that the perspective drawing is correct or accurate. Then, using the three-dimensional space thus defined, (1) a method of forming a three-dimensional or stereoscopic image by a method like a triangulation method, from two or more sketches having different lines of sight or different views, (2) a method in which a three-dimensional shape analogous to that in a perspective drawing is searched for, and the analogous three-dimensional shape is deformed by a neural network, or the like, so as to create a three-dimensional or stereoscopic image in accordance with the perspective drawing, or (3) a method in which a single plane view is human-created in a CAD (Computer-Aided-Design) way, and is combined with lines of a perspective drawing, for example, is carried out.
However, since the sketch created by a designer, or the like, is not necessarily drawn in accordance with an accurate orthogonal coordinate system, the coordinate system is often greatly distorted by the image possessed by the designer. Therefore, when three-dimensional shape data is generated in the three-dimensional space of the orthogonal coordinate system as in the above-described related art, the three-dimensional shape data may not appropriately reflect the image intended by the designer.
In view of the related art as described above, the inventors of this application has proposed a method for creating three-dimensional shape data, by associating two-dimensional points and axes in a sketch drawn by a designer, etc., with points and axes set in a three-dimensional space, using an angle method, so as to determine the viewpoint position and converting a three-dimensional object in the sketch into three-dimensional form, as disclosed in Japanese Patent No. 4397372 (JP-B-4397372). In this manner, three-dimensional shape data can be generated which appropriately reflects the concept or image possessed by the designer and expressed in the sketch.
Regarding determination of the viewpoint position, Japanese Patent Application Publication No. 2000-76453 (JP-A-2000-76453) discloses a method in which a still image (sketch) drawn by a designer, or the like, is retrieved, and the viewpoint is found or determined based on the positional relationship of straight lines in the retrieved still image (sketch).
In the meantime, in connection with determination of the viewpoint position according to the method as disclosed in JP-B-4397372, a solution obtained by the angle method (and the disclosed three-point method) is not a general solution, but a special solution for which equations need to be individually expanded or developed. Therefore, it is necessary to formulate equations for each sketch drawn by a designer, or the like, and to determine whether an appropriate solution is obtained, and it may be time-consuming to accomplish these tasks.
Also, in the method as disclosed in JP-B-4397372, creation of image lines, generation of cross-section lines, generation of spatial lines, and creation of curved surfaces are sequentially carried out. Therefore, the user needs to select (designate) the same line at many times, for example, and there is room for improvement in the operational efficiency, namely, it is desirable to reduce the complexity in operation.
Furthermore, in the method as disclosed in JP-B-4397372, two-face filleting (rounding) for creation of a curved surface is carried out simply utilizing the known CAD function. In this case, if a fillet portion is formed by arcs, a difference in the curvature appears in the created curved surface, thus making it impossible to create a high-quality curved surface. In order to avoid the appearance of such a difference in the curvature, the user needs to designate a beginning line and an ending line of the fillet portion, and designate a sweep cross-section, resulting in deterioration of the operational efficiency.